Bi-directional stiffness for optical image stabilization in a dual-aperture digital camera

ABSTRACT

Mechanisms for providing optical image stabilization in at least one direction as well as auto-focus in a digital camera comprise a plurality of springs mechanically coupled to at least a lens module carrying a lens of the digital camera, wherein the plurality of springs provides overall low stiffness to movement of the lens in two, first and second directions orthogonal to each other, and provides high stiffness to torsion of the lens module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application from U.S. patentapplication Ser. No. 15/310,887 filed Nov. 14, 2016 (now allowed), whichwas a 371 application from international patent applicationPCT/IB2016/053026, and is related to and claims priority from U.S.Provisional Patent Application No. 62/167,571 filed on May 28, 2015which is expressly incorporated herein by reference in its entirety.

FIELD

Embodiments disclosed herein relate in general to digital cameras and inparticular to optical image stabilization (OIS) and auto-focus (AF) insingle and/or dual-aperture (“dual-optical module”) digital cameras.

BACKGROUND

In recent years, mobile devices such as cell-phones (and in particularsmart-phones), tablets and laptops have become ubiquitous. Most of thesedevices include one or two compact cameras: a main rear-facing camera(i.e. a camera on the back side of the device, facing away from the userand often used for casual photography) and a secondary front-facingcamera (i.e. a camera located on the front side of the device and oftenused for video conferencing).

Although relatively compact in nature, the design of most of thesecameras is very similar to the traditional structure of a digital stillcamera, i.e. they comprise an optical component (or a train of severaloptical elements and a main aperture) placed on top of an image sensor.The optical component (also referred to as “optics”) refracts theincoming light rays and bends them to create an image of a scene on thesensor. The dimensions of these cameras are largely determined by thesize of the sensor and by the height of the optics. These are usuallytied together through the focal length (“f”) of the lens and its fieldof view (FOV)—a lens that has to image a certain FOV on a sensor of acertain size has a specific focal length. Keeping the FOV constant, thelarger the sensor dimensions (e.g. in a X-Y plane) the larger the focallength and the optics height.

In addition to the optics and sensor, modern cameras usually furtherinclude mechanical motion (actuation) mechanism for two main purposes:focusing of the image on the sensor and optical image stabilization(OIS). For focusing, in more advanced cameras, the position of the lensmodule (or at least one lens element in the lens module) can be changedby means of an actuator and the focus distance can be changed inaccordance with the captured object or scene. In these cameras it ispossible to capture objects from a very short distance (e.g., 10 cm) toinfinity. The trend in digital still cameras is to increase the zoomingcapabilities (e.g. to 5×, 10× or more) and, in cell-phone (andparticularly smart-phone) cameras, to decrease the pixel size andincrease the pixel count. These trends result in greater sensitivity tohand-shake or in a need for longer exposure time. An OIS mechanism isrequired to answer the needs in these trends.

In OIS-enabled cameras, the lens or camera module can change its lateralposition or tilt angle in a fast manner to cancel the handshake duringthe image capture. Handshakes move the camera module in 6 degrees offreedom, namely linear movements in three degrees of freedom (X, Y & Z),pitch (tilt around the X axis), yaw (tilt around the Y axis) and roll(tilt around the Z axis). FIG. 1 shows an exemplary classical fourrod-springs (102 a-d) OIS structure in a single-aperture camera module100. The four rod-springs are rigidly connected to an upper frame 104that usually accommodates an AF actuator (not shown) that moves the lensmodule 106. This structure allows desired modes of movement in the X-Yplane (translation), FIG. 1a , but also allows a mode of unwantedrotation (also referred to as “0-rotation” or “torsion”) around the Zaxis, FIG. 1b . The latter may be due to a combination of several causessuch as asymmetric forces applied by the coils or by a user's (or phone)movements, imperfections of the rod-springs and the high rotationalcompliance of the four spring rod spring+frame structure.

In the case of a centered single-aperture camera module, this rotationdoes not affect the image quality severely, since the lens isaxisymmetric. However, this does affect OIS in a dual-camera module,FIGS. 2a and 2b . FIG. 2a shows a rotation mode around an axis 202roughly centered between two camera modules 204 and 206 of adual-aperture camera 200.

Because of the location of rotation axis 202, the rotation may causesignificant deterioration in the image quality. The rotation causes eachlens to shift away in undesired directions (shown by arrows in FIG. 2b), without having any ability to predict when and if this may happen.The result is motion blur of the image and a shift of the two lenses inopposite Y directions caused by the unwanted rotation that results indecenter between images received by each camera module, and thereforepotentially in a catastrophic influence on fusion algorithm results.

Yet another problem may occur in a folded optics zoom dual-aperturecamera, such as a camera 300 shown in FIG. 3. Such a camera is describedfor example in detail in co-owned international patent applicationPCT/IB2016/052179 which is incorporated herein by reference in itsentirety. Camera 300 comprises a folded optics camera module 302 and anupright (non-folded) camera module 304. Among other components, foldedoptics camera module 302 comprises a lens actuation sub-assembly formoving a lens module 306 (and a lens therein, which is referred tohenceforth as “folded lens”) in the X-Y plane. The lens actuationsub-assembly includes a hanging structure with four flexible hangingmembers (i.e. the “rod-springs” referred to above) 308 a-d that hanglens module 306 over a base 310. In some embodiments, hanging members306 a-d may be in the form of four wires and may be referred to as “wiresprings” or “poles”. The hanging structure allows in-plane motion asknown in the art and described exemplarily in co-owned U.S. patentapplication Ser. No. 14/373,490. Exemplarily, a first movement direction312 of the lens is used to achieve Auto-Focus (AF) and a second movementdirection 314 is used to achieve OIS. A third movement, an unwantedrotation 316 of the lens about an axis parallel to the Z axis asdescribed above actually causes an unwanted effect of dynamic tilt ofthe lens (the lens' optical axis may not be perpendicular to thesensor's surface due to that rotation) and may result in images that areusually sharp on one side and blurry on the other side.

The physical quantities that reflect the tendency of any structure todynamically behave one way or another are the natural frequency valuesthat characterize each mode of behavior. This is of course also relevantfor the hanging structure described above. FIGS. 4(a)-(c) show thesimulated behavior of a standard rigid plate supported by four roundrod-spring poles. The rigid plate may represent any optical element(such as, for example, a lens). The rod-spring poles have the samerigidity to movement in any direction in the X-Y plane (which isperpendicular to the pole's neutral axis). The figures show thecompliance of the structure expressed in terms of a natural frequencyratio for each different movement mode: FIG. 4a refers to X-translation,FIG. 4b refers to Y-translation and FIG. 4c refers to rotation aroundthe Z axis. The arrows show schematically the different movements. Thereference bar indicates deformation scale in millimeters. The normalized(relative to the first frequency which in this exemplary case is of 33.6Hz) natural frequencies for X and Y translations are of the same order(specifically 1 in (a) and 1.1 in (b)), whilst the natural frequency forrotation (c) has a relative value of 1.8, which is also of the sameorder of the X and Y translations. Thus the ratio between naturalfrequencies for torsion (rotation around Z) and for X or Y translationis about 1.8. In general, known ratios are no larger than 2. This meansthat the chance that the torsion mode will arise is almost the same asthe chance that the X and Y translation modes will arise. This may causeproblems in dual-aperture and/or folded zoom cameras (where it will beexpressed as dynamic tilt) as described above.

In view of the above, it would be very difficult to get the desiredmovement of the lens without an active control loop (having such acontrol loop is one possible way to overcome the described problems).The unwanted torsion may be reduced significantly by means of electricalcontrol over the force applied by the coils (i.e. by using several coilsand controlling them so the resultant torque acts to limit the rotationof the lens within specified acceptable limits). However, the additionof an active control loop to avoid tilt complicates the design and addsto cost. It would be therefore advantageous to have lens actuationsub-assemblies for OIS without an active control loop for rotation/tilt.

SUMMARY

In an exemplary embodiment, there is provided a mechanism for providingoptical image stabilization (OIS) in at least one direction in a digitalcamera, comprising: a plurality of springs mechanically coupled to atleast a lens module carrying a lens of the digital camera, wherein theplurality of springs provides overall low stiffness to movement of thelens module in two, first and second directions orthogonal to each otherand high stiffness to torsion of the lens module such that a ratiobetween natural frequencies arising from the high stiffness and the lowstiffness is greater than 2.

In an exemplary embodiment, the plurality of springs includes a firstplurality of springs with low stiffness in the first direction and highstiffness in the second direction; and a second plurality of springswith high stiffness in the first direction and low stiffness in thesecond direction.

In an exemplary embodiment, the ratio between natural frequenciesarising from the high stiffness and the low stiffness is greater than 3.

In an exemplary embodiment, the ratio between natural frequenciesarising from the high stiffness and the low stiffness is greater than 5.

In an exemplary embodiment, the ratio between natural frequenciesarising from the high stiffness and the low stiffness is greater than10.

In an exemplary embodiment, the mechanism is dimensioned to accommodatethe lens module without obstructing an optical path passing through thelens.

In an exemplary embodiment, the first plurality includes two pairs ofleaf springs and the second plurality includes a pair of cross springs.

In an exemplary embodiment, the first plurality includes a pair of leafsprings and one cross spring and the second plurality includes a pair ofcross springs.

In an exemplary embodiment, each of the first and second pluralitiesincludes a pair of cross springs.

In an exemplary embodiment, the digital camera is a dual-optical modulecamera.

In an exemplary embodiment, the lens is a folded lens.

In an exemplary embodiment, the camera is adapted to perform auto-focus.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of embodiments disclosed herein are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. The drawings and descriptions are meant toilluminate and clarify embodiments disclosed herein, and should not beconsidered limiting in any way. Like elements in different drawings maybe indicated like numerals.

FIG. 1 shows a camera module with an exemplary classical fourrod-springs OIS structure: (a) modes of wanted X-Y translations, and (b)mode of unwanted rotation around the Z axis;

FIG. 2 shows a dual-aperture camera: (a) rotation mode around an axisroughly centered between two camera modules, and (b) movement of eachlens in undesired directions;

FIG. 3 shows a dual-camera module with a folded optics camera module;

FIG. 4 show the simulated behavior of a standard rigid plate supportedby four round rod-spring poles: (a) movement in the X-direction, (b)movement in the Y direction and (c) tilt around a rotation axis;

FIG. 5 shows an exemplary embodiment of an OIS and AF support structuredisclosed herein in a folded optics camera module in (a) an isometricview, (b) side view and (c) radial cross section;

FIG. 6 shows the simulated behavior of the support structure of FIG. 5for (a) movement in the X-direction, (b) movement in the Y direction and(c) tilt around a rotation axis.

FIG. 7 shows an isometric view of another exemplary embodiment of an OISand AF support structure in a folded optics camera module;

FIG. 8 shows an isometric view of an exemplary embodiment of adual-aperture camera with two camera modules held by a support structuredisclosed herein;

FIG. 9 shows the simulated behavior of another exemplary embodiment of asupport structure in a folded optics camera module for (a) movement inthe X-direction, (b) movement in the Y direction and (c) tilt around arotation axis.

DETAILED DESCRIPTION

We have determined that lens support structures used for AF and OIS maybe designed with support members that have different compliance(stiffness) to movements in different directions of different types ofmovements. The different compliance in different movement directions orfor different movement types may be obtained by non-round or non-squaresupports cross sections of such support members.

FIG. 5 shows an exemplary embodiment of a folded lens 500 held by asupport structure numbered 502 in (a) an isometric view, (b) side viewand (c) radial cross section. Exemplarily, support structure 502 maycomprise four support spring members 502 a-d, each spring member beingessentially a thin leaf spring with high stiffness in one direction(e.g. Y) and low stiffness in a second direction (e.g. X) perpendicularto the first direction. In this description, the term “high stiffness”used with reference to a spring structure refers to a spring structurehaving a natural frequency in the range of hundreds to thousands ofHertz, exemplarily between 200-4000 Hz. The term “low stiffness” usedwith reference to a spring structure refers to a spring structure havinga natural frequency in the range of tens of Hertz, exemplarily between30-100 Hz. In general, the natural frequency of a spring is proportionalto the square root of its stiffness.

Henceforth, support members 502 are referred to as “leaf springs”.Exemplarily, a leaf spring 502 has a length L3 of 4.8-5.5 mm and arectangular cross section, with a small (exemplarily 20-60 μm) thicknessd₁ in the flexing direction (here X) and with a significantly larger(exemplarily 0.5-1 mm) width d₂ in the non-flexing direction (here Y).The structure and mechanical properties of the leaf springs allows onlymovement for AF in the X direction. Each leaf spring is rigidlyconnected at a respective upper end 504 a-d to a rigid upper frame 506and at a respective bottom end to a base such as base 310. Leaf springs502 a and 502 b may optionally be connected at a bottom end by a bar530. Support structure 502-further comprises two support springs 508 aand 508 b coupled rigidly to frame 506 at an upper end 510 and to a lenssupport plate 512 at a lower end (respectively 514 a and 514 b). Supportsprings 508 a and 508 b are designed to have low stiffness in the Ydirection for OIS movement, and high stiffness in the X direction, whilenot adding significantly to the camera module width. Exemplarily and asshown separately, springs 508 a or 508 b include two leaf spring members520 and 521 connected by two diagonal leaf spring members 522 and 524.The leaf springs and diagonal springs are connected at an upper end to amember 523. Hereinafter, a support spring such as a spring 508 isreferred to as “cross spring”. Exemplarily, a diagonal leaf springmember has a rectangular cross section with a thickness of the sameorder of that of a leaf spring 502 (exemplarily 20-60 m) and a width d₃of about 0.2 mm. Exemplarily, a cross spring 508 may have a lengthdimension L4 in the range of 7-10 mm and a height H in the range of 4-5mm. Exemplarily in an embodiment, L4 is approximately 9.5 mm and H isapproximately 4.6 mm. Optionally or alternatively, leaf springs 502 aand 502 b may be replaced by a cross spring 508, with care being taken(if necessary) not to obstruct an optical path. In yet anotheralternative embodiment, a cross spring 508 may also replace leaf springs502 c and 502 d, with care being taken (if necessary) not to obstruct anoptical path.

Frame 506 may exemplarily be made of a plastic material such as LCP(VECTRA® E525T). Plate 512 is rigidly connected to a lens 516 (or to alens carrier carrying the lens). In this embodiment, upper frame 506 hasa U-shape so as not to block an optical path to a path-folding opticalelement (e.g. mirror or prism, not shown). Exemplarily, frame 506 hasdimensions of L₁=11.9 mm and L₂=7.6 mm. More generally, the ratio L₂/L₁can be between 0.5-0.7.

FIG. 6 shows the first three modes of the support structure of FIG. 5resulting from modal Finite Element Analysis where: (a) describes a modeof movement in the X-direction for AF, (b) describes a mode of movementin the Y direction for OIS and (c) describes a mode of (unwanted) tiltaround a rotation axis like movement 316 thin FIG. 3. The arrows showschematically the different movements. In use for AF, the lens and upperframe 506 is actuated to move in the X direction while flexing springs502. Movement in the Y direction and unwanted rotation such a rotation316 around the Z-axis in FIG. 3 are minimal. For OIS, lens movement inthe Y direction is allowed by the flexing of cross springs 508 (see alsoFIG. 6b ), while movement in the X direction and unwanted rotationaround the Z-axis are again minimal. Specifically, the normalized(relative to a first frequency which in this exemplary case is of 40 Hz)natural frequencies for X and Y translations are of the same order(specifically 1 in (a) and 1.2 in (b)), whilst the natural frequency forrotation (c) has a relative value of 29.3. That is, the naturalfrequency in FIG. 6c is of a significantly higher order than that inFIGS. 6a and 6b . Advantageously, the arrangement of separate leafsprings (flexible in the X-direction) and cross springs (flexible in theY direction) prevents unwanted rotation motion around the Z-axis.

In an embodiment and exemplarily, the springs are made of acopper-nickel-tin mx-215 alloy with an elastic modulus of 125 GPa. Inother exemplary embodiments, the springs may be made of some other metalalloy or of a non-metal, for example of polymer or plastic material, acomposite material or a combination of metal/ceramic and/or plasticmaterials, chosen such that the dimensions and elastic properties fitthe camera form requirements.

FIG. 7 shows an isometric view of another exemplary embodiment of asupport structure in a folded optics camera 700. Here, an upper frame706 is closed and leaf springs 702 c and 702 d are connected at thebottom by a bar 704, imparting added stiffness in the Y direction.Alternatively, the leaf springs and bar may be replaced by a crossspring. The frame is closed behind the optical path folding element(prism or mirror) so there is no problem of disturbing the optical pathto this element. In yet another embodiment shown in FIG. 9, an upperframe 906 has a closed rectangular shape strengthened by two cross barmembers 906 a and 906 b.

FIG. 8 shows an isometric view of an exemplary embodiment of adual-aperture camera 800 with two camera modules 802 and 7804 held by asupport structure disclosed herein. An upper frame 806 is closed likeframe 706 in FIG. 7, while the support structure is comprised of crosssprings 808 a-d. Here, the support structure is designed for OIS in twodirections—X and Y.

FIG. 9 shows the first three modes of another exemplary embodiment of asupport structure in a folded optics camera module, as resulting frommodal simulation, where: (a) describes a mode of movement in theX-direction for AF, (b) describes a mode of movement in the Y directionfor OIS and (c) describes a mode of (unwanted) tilt around a rotationaxis. The arrows show schematically the different movements. The firstfrequency is 100 Hz, and the normalized natural frequencies for X and Ytranslations are of the same order (specifically 1 in (a) and 1.2 in(b)), whilst the natural frequency for torsion (c) has a relative valueof 23.9.

In summary, the performance of the support structures provided herein interms of avoidance of unwanted linear movement and rotation (torsion)while performing AF and OIS is much superior to that of any knownsupport structure used for the same purposes.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.The disclosure is to be understood as not limited by the specificembodiments described herein, but only by the scope of the appendedclaims.

What is claimed is:
 1. A mechanism for providing optical imagestabilization (OIS) in a digital camera, comprising: a first pluralityof springs connected at a lower end to a base and at an upper end to arigid upper frame, the first plurality of springs enabling the rigidupper frame to move with a first stiffness in a first direction and tomove with a second stiffness, higher than the first stiffness, in asecond direction orthogonal to the first direction; and a secondplurality of springs connected at an upper end to the rigid upper frameand at the lower end to a lens, the second plurality of springs enablingthe lens to move with a third stiffness in the second direction and tomove with a fourth stiffness, higher than the third stiffness, in thefirst direction, wherein the mechanism enables lens movement in thefirst and second directions and reduces rotation about an axisperpendicular to the first and second direction.
 2. The mechanism ofclaim 1, wherein normalized natural frequencies for the first directionand second direction are of the same first order of magnitude andwherein a normalized natural frequency for rotation has a value which isgreater by at least one order of magnitude than the first order ofmagnitude.
 3. The mechanism of claim 1, wherein a ratio between anatural frequency for rotation and either of the natural frequencies formovement in the first direction and the second direction is greater than2.
 4. The mechanism of claim 1, wherein a ratio between a naturalfrequency for rotation and either of the natural frequencies formovement in the first direction and the second direction is greater than5.
 5. The mechanism of claim 1, wherein a ratio between a naturalfrequency for rotation and either of the natural frequencies formovement in the first direction and the second direction is greater than10.
 6. The mechanism of claim 1, dimensioned to accommodate the lensmodule without obstructing an optical path passing through the lens. 7.The mechanism of claim 1, wherein the first plurality of springs or thesecond plurality of springs includes a pair of cross springs.
 8. Themechanism of claim 1, wherein the first plurality of springs and thesecond plurality of springs includes a mix of leaf springs and crosssprings.
 9. The mechanism of claim 1, wherein the first plurality ofsprings includes two pairs of leaf springs and wherein the secondplurality of springs includes a pair of cross springs.
 10. The mechanismof claim 1, wherein the first plurality of springs includes a pair ofleaf springs and one cross spring and wherein the second plurality ofsprings includes a pair of cross springs.
 11. The mechanism of claim 1,wherein each of the first and second pluralities of springs includes apair of cross springs.
 12. The mechanism of claim 1, wherein the digitalcamera is a dual-optical module camera.
 13. The mechanism of claim 1,wherein the lens module is a folded lens module.
 14. The mechanism ofclaim 1, adapted to perform auto-focus.
 15. The mechanism of claim 5,wherein the lens movements in the first direction and the seconddirection are characterized by natural frequencies in the range of30-100 Hz and wherein the lens rotation about an axis perpendicular tothe first direction and the second direction is characterized by anatural frequency in the range of 200-4000 Hz.
 16. The mechanism ofclaim 1, wherein the second stiffness is greater than the firststiffness by at least 4 times and wherein the fourth stiffness isgreater than the third stiffness by at least 4 times.
 17. The mechanismof claim 1, wherein each spring of the first plurality of springs has arectangular cross section with 20-60 μm thickness in the firstdirection, and wherein each spring of the second plurality of springshas a rectangular cross section with 20-60 μm thickness in the seconddirection.
 18. The mechanism of claim 12, wherein the second pluralityof springs is connected at the upper end to the rigid upper frame and atthe lower end to two lenses of the dual-optical module camera